1. Field of the Invention
The present invention relates to gas generators or inflators that utilize the combustion of a solid fuel gas generant composition for the generation of a gas for the rapid inflation of vehicle passive restraint inflatable crash protection bags, and more particularly to an improved housing construction for such generators.
2. Description of the Prior Art
Many forms of gas generators or inflators that utilize combustible solid fuel gas generant compositions for the inflation of inflatable crash protection or "air bag" restraint systems are known in the prior art. One form of such gas generator includes as main component parts a concentric arrangement of annular combustion chambers bounded by an outer casing or housing structure, as disclosed in U.S. Pat. No. 4,296,084, granted to G. V. Adams and F. E. Schneiter and assigned to the assignee of the present invention. The combustion chamber encloses a rupturable container or cartridge that is hermetically sealed and contains therein solid gas generant material in pelletized form, surrounded by an annular filter. The generator further includes a central ignition or initiator tube, and an annular or toroidal filter chamber adjoining and encircling the combustion chamber with an inner casing or housing structure in close surrounding and supporting relationship to the rupturable container, the inner casing being formed by a cylinder having uniformly spaced peripheral ports or orifices near one end. These orifices provide exit holes for the flow of inflation gas from the combustion chamber.
Gas generators must withstand enormous thermal and mechanical stresses for a short period during the gas generation process. Accordingly, gas generators in current use for filling automobile or other vehicle crash bags have been very heavy, being fabricated from thick-walled steel for the casing and other housing structural components, with the structural components being joined together by screw threads, roll crimping or welding.
Recent emphasis, however, on weight reduction in automobiles has created a need, and a demand, for a lighter weight crash bag gas generator. This is of particular importance in a system for driver crash protection where the gas generator is mounted on the steering wheel where bulk becomes a factor and the availability of a lighter weight generator enables a reduction to be made in the weight of the steering wheel and steering column on which the generator is mounted.
An improvement in gas generators of the type disclosed in U.S. Pat. No. 4,296,084 is disclosed and is being claimed in pending U.S. application Ser. No. 595,774, filed Apr. 2, 1984 by G. V. Adams and W. J. Ahlf and assigned to the assignee of the present invention. In application Ser. No. 595,774 there is provided an improvement that facilitates the substitution of aluminum for the steel structural components of the prior art, and hence, enables a significant reduction in the weight of the gas generator to be made. Specifically, there is provided a housing construction comprising two subassemblies, specifically, first and second aluminum structural components, the first component being a diffuser shell and the second a base shell. The first structural component or diffuser shell has three integrally formed concentric cylinders which form the generator structural walls and define chambers therein containing the solid fuel or gas generant, ignition materials, and filters and provide exit openings or port holes for the passage of inflation gases from chamber to chamber and into the protective air bag. The second structural component or base shell contains an electric initiator and generator attachment flange and provides three concentric mating surfaces for the diffuser shell. The three concentric cylinders of the diffuser shell are simultaneously joined to the concentric mating surfaces of the base shield by a single inertia welding operation thereby facilitating the manufacture of the gas generator on a large scale, inexpensively.
The prior art gas generators, however, are characterized by concentric sequential arrangements of the igniter, the solid fuel, the filtering means and the cooling means. Such structures have certain disadvantages in that they tend to be bulky and heavier than desirable, and require the joining together in a sealing manner of three concentric mating surfaces. The prior art structures tend to be bulky and heavier than desirable because for a given generator outer housing height and diameter, the maximum volume for the solid fuel is not obtained with the described sequential arrangement of the solid fuel, the filter means and the cooling means. Thus, for a given charge of solid fuel a greater generator outer housing height is required than would be the case were the structural arrangement such that maximum volume for the solid fuel were obtained.